In digital wireless communications systems, two devices in communication with each other must generally perform timing and carrier frequency synchronization in order to detect and process information that is being transmitted between them. For example, a receiver generally needs to synchronize (sometime also referred to as “acquire” or “lock”) its reference (digital demodulator) clock and (carrier) frequency, as provided by a local oscillator (LO) to signals transmitted thereto by a transmitting device, in order to properly process the information contained in such signals.
Some past techniques for synchronization have included sweeping or stepping a clock or local oscillator until a lock is detected; using a decision directed technique; using a Costas loop (for carrier frequency); squaring magnitudes (clock timing) based feedback; and differential sync vector measurement (carrier frequency).
One prior technique for obtaining frequency and timing synchronization is to provide a synchronization word or value in a packet, and use the phase difference (in spatial or vector domain) between two or more such values as an indicator for how much to adjust, for example, a local oscillator to be synchronized with the carrier frequency of the received signal.
FIG. 1 is a diagram of a data packet having sync words, according to the prior art. As shown, a data packet 100 includes a synchronization (or “sync”) word 102 and a synch word 104. Using prior techniques, the relative vector/spatial phase difference between synch words 102 and 104 may be determined and used for synchronization.
Unfortunately, in a number of wireless communication systems, carrier frequency may be relatively far off at a receiver, especially in high frequency systems where the ratio between the carrier frequency and symbol rate of a transmitted signal is high. Also, if a synch word is large (e.g., 100's of symbols in length), the phase difference may become so large that such prior techniques may not provide adequate results. As a result, such past synchronization techniques may require iteration or “sweeping” for timing and frequency detection, and thus may not provide satisfactory performance in some situations.
Thus, what is needed is an improved system and method for providing timing and frequency synchronization that does not suffer from the drawbacks of past methods and systems.